Numerical Simulation of Ice Particle Growth in a Cloud of Supercooled Water Droplets

Abstract

An empirical approximation is presented for estimating the growth of ice crystals by diffusion. The approximation is valid for computing crystal growth under conditions of constant temperature and water saturation. Crystal growth in these conditions has been realistically simulated for a period of 30 min in the range of temperatures from ?1 to ?30C. Modifications to the approximation are presented which permit it to he applied to varying temperature and varying saturation. The approximation for diffusion growth was coupled with an approximation for accretion growth to simulate ice particle growth by diffusion plus accretion. These calculations indicated that 1-?m ice crystals could grow to a size sufficient to collect supercooled droplets within a period of roughly 2 min regardless of the temperature and liquid water content conditions. The calculations also indicated that 1-cm hail could form from 1-?m ice crystals in roughly 27 main. The hail was calculated to form in a cloud of supercooled droplets containing 3.0 gm m?3 of liquid water at a temperature of ?15C.